JPH03111435A - Styrene resin foam excellent in post expansion properties - Google Patents

Abstract

PURPOSE:To prepare a styrene resin foam excellent in the post expansion properties and giving a molded foam excellent in the strengths by controlling the wt.-average mol.wt. and the ratio of the initial relaxation modulus in stress relaxation at 120 deg.C to that at 150 deg.C of a styrene resin each to be in a specified range. CONSTITUTION:A styrene resin foam is prepd. from a styrene resin having a wt.-average mol.wt of 150000-500000 and a ratio of the initial relaxation modulus in stress relaxation at 120 deg.C to that at 150 deg.C of 1-2.5. In the post expansion process, the foam has a good fit to a mold, shows neither split nor scablike surface even when the heating time is too short, and hardly gives a molded product accompanied by a permanent distortion of keloidal surface even with a too long heating time. This resin is prepd. by polymerizing a styrenic monomer in the presence of an initiator comprising a low-temp. decomposable org. peroxide having at least three repeating units of the formula (wherein (l), (m), and (n) are each 1-20; and R1 to R4 are each H, 1-5C alkyl, cyclohexyl, or phenyl).

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a styrenic resin foam that has excellent heat secondary foaming moldability and excellent strength of the foam molded product.

(Prior art and problems) Styrenic resin foam can be secondary-foamed by heating and easily molded into a desired shape, and the resulting molded product is lightweight, has excellent mechanical strength, and has a beautiful appearance. Because it is highly hydrophobic and has excellent heat insulation, it is used in food packaging materials such as boxes, trays, and cups, as well as simple containers.

Recently, styrenic resin foams with good secondary foaming moldability have been desired from the viewpoint of improving productivity and reducing defective rates.

In the production of a series of heated secondary foamed products, in which sheet-shaped styrene resin foam is heat-treated in a heating furnace to foam, then taken out of the heating furnace and molded in a mold, the temperature inside the heating furnace is constant. Due to uniformity and fluctuations in the temperature inside the furnace due to outside air temperature, some or all of the sheet may be underheated, causing the sheet to tear during molding, or part of the surface of the molded product to form a crust. The moldability may deteriorate, or conversely, heating may become excessive, resulting in formation of keloids on the surface of the molded product, or variations in the thickness of the molded product.

In order to prevent the formation of keloids, there are known methods such as increasing the molecular weight of the base polystyrene polymer, applying a film to the sheet surface, and forming a layer with high resin density, the so-called skin layer. However, with this method, it is difficult to obtain a foam with a well-defined shape, and sheet tearing is likely to occur, especially in the case of a deep-drawn product.

In addition, in order to obtain a foam with good shapeability, methods are known in which the molecular weight of the polystyrene polymer base material is lowered or plasticizers, lubricants, etc. are added to the polystyrene polymer base material. , keloid-like defects that occur during overheating during secondary molding are likely to occur.

The use of a styrene resin foam with a wide molecular weight distribution is effective as a method for suppressing the occurrence of keloids and obtaining a styrenic resin foam with good moldability.
It is described in Japanese Patent Application Laid-Open No. 62-22834. However, such molded products made of styrene resin foams having a wide molecular weight distribution inherently have a drawback of low strength.

(Means for Solving the Problems) In view of the current situation, the present inventors introduced a long alkyl chain into a styrene polymer to suppress the formation of keloids during secondary heat molding. As a result of intensive studies to develop a styrenic resin foam that has good shaping properties and excellent deep drawability, the present invention has been completed.

That is, the present invention has; (i) a weight average molecular weight of 150,000 to 500,000, and 120
Initial relaxation modulus of stress relaxation measured at °C and 150″C
The ratio of the initial relaxation modulus of stress relaxation measured at is 1 to 2.5.
The object of the present invention is to provide a styrenic resin foam having excellent secondary moldability within the range of .

In addition, ■ The thickness of the styrene resin foam is 0°5~5■
It is also a styrenic resin foam with excellent secondary moldability, which is in the form of a sheet with a bulk density of 0.03 to 0.3 g/cm3.

The present invention will be explained in more detail below.

The weight average molecular weight of styrene resin foam is 150,000 to 50
If the weight average molecular weight is less than 150,000, the strength of the foamed molded product will be weak and cannot be used in practical use. The moldability during the subsequent foam molding becomes significantly worse.

In addition, in the present invention, the molecular weight of the styrene polymer that is the foam base material is determined by GPC measurement method using GP manufactured by Toyo Soda Kogyo.
C (HLC-802A), the same company's GPC column (T
SK-C, EL-C; two MHs were used).

The styrenic resin foam of the present invention has a ratio of the initial relaxation modulus of stress relaxation measured at 120°C to the initial 1 tlltil sum elastic modulus of stress relaxation measured at 150°C of 1 to 2.
5, more preferably 1.
It is in the range of 2 to 2.3.

If the ratio of 120°C/150°C is less than 1, the moldability of the secondary foamed product will be poor, and if it exceeds 2.5, the deep drawability during secondary foaming will be poor.

Note that the initial relaxation modulus of stress relaxation is measured according to the method described in Katsuyama et al., No. 71 S4, pages 540-545 (1968).

First time here! The IJII sum modulus refers to the relaxation modulus obtained at the moment of applying strain. If the sample to be used is a foam, the air bubbles should be removed beforehand to make it solid. Pellets before foaming may be used.

Initial relaxation modulus of stress relaxation measured at 120″C and 15
The ratio of the initial relaxation modulus of stress relaxation measured at 0 °C is 1
A styrenic resin having a molecular weight in the range of 2.5 to 2.5 can be prepared, for example, as follows, but is not limited thereto.

- Formula (■): (In the formula, l, m, and n are integers from 1 to 20, and R+,
Rz, R3, and R- are hydrogen, an alkyl group having 1 to 5 carbon atoms, a cyclohexyl group, or a phenyl group. ) 3 or more repeating units, preferably 5 to 30 repeating units
A styrenic monomer is polymerized using a low-temperature decomposable organic peroxide initiator having

As such an initiator, for example, those having the following repeating units can be used.

By employing such a polymerization method, a styrenic polymer into which a long-chain alkyl group is introduced is produced.

In this case, during polymerization, prepolymerization is carried out at a temperature in the range of (initiator's 10-hour half-life temperature) to (initiator's 10-hour half-life temperature + 70°C) until the polymerization rate reaches at least 10% by weight. By carrying out the above steps and then proceeding with the polymerization at an arbitrary temperature, a long alkyl chain can be suitably introduced into the styrenic polymer.

Although long alkyl chains can be introduced into the styrenic polymer of the present invention by the method described above, the polymerization method is not particularly limited. Known methods such as bulk polymerization, solution polymerization, and suspension polymerization can be used. In addition, it may be used in combination with a known organic peroxide, or it may be added during the process.
A solvent or the like can also be used.

Styrene monomers used include styrene, α-
Methylstyrene, vinyltoluene, p-methylstyrene, etc. can be used alone or in combination. In addition, a vinyl monomer such as acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, or maleic anhydride may be used in combination with the styrene monomer of the present invention, if necessary.

In particular, the polymerization conditions should be adjusted so that the molecular weight is adjusted, and the oligomer content (vinyl oligomers such as styrene dimers and dimers) is as low as possible. It is 0.5% by weight or less.

Oligomer content can be measured by gas chromatography or liquid chromatography. Furthermore, if necessary, a lubricant, a plasticizer such as mineral oil, an antioxidant, etc. may be included.

The styrenic resin having a long alkyl chain was quantified as follows.

After dissolving the styrenic polymer foam in 10 times the amount of methyl ethyl ketone, the same amount of methanol is slowly added to precipitate the styrenic polymer.

The precipitated styrenic polymer is dried at 200° C. under reduced pressure of 15 s Hg for 30 minutes. Using this styrene polymer, 13C is measured using JNM-GX270 manufactured by JEOL Ltd. Measurement was performed under the following measurement conditions.

Complete decoupling mode - 45° pulse, observation frequency = 67.8MH2, waiting time - 2.5 seconds, number of scans = ioo, ooo times, sample concentration = l Qwt%, solvent = 1.1-tetrachloroethane (d2) , Sample tube-10, Measurement temperature = 120° C0 A peak derived from the carbon of the methylene group of the long alkyl chain appears at 29.4 ppm. Furthermore, a peak derived from the carbon adjacent to the quaternary carbon in the long chain appears at 33.7 ppm. By confirming the presence of this peak, it is possible to confirm the presence or absence of the structural unit (1) in the styrenic polymer.

As another measurement method, it is also possible to perform DSC analysis using DSC-41 manufactured by Shimabara Seisakusho and determine the Tg of the styrene polymer that is the foam base material. “C-NMR
The measurement is carried out using a sample treated in the same manner as in the measurement, at a heating rate of 8°C/min.

Styrenic resin foam uses styrene resin and propane.
Either blowing agents such as lower hydrocarbons such as butane, pentane, and hexane or halogenated hydrocarbons such as methyl chloride, dichloromethane, trichloromonofluoromethane, and dichlorodifluoromethane are impregnated and fed to an extruder, or styrene resin is After supplying the foaming agent to the extruder, the foaming agent is press-fitted into the extruder, the foaming agent and styrene resin are melted and kneaded in the extruder, and the thickness is increased by a known method such as extruding from a T-die or circular die. Saga 0.5-5IIIli1
A sheet-like primary foamed polystyrene foam having a bulk density of 0.03 to 0.3 g/c is produced.

- The thickness of the post-foamed sheet is preferably 0.5 to 5 mm. If the thickness is thinner than 0.58, the sheet may be damaged during the post-foaming or the molded product will not have sufficient strength. Further, if the thickness exceeds five layers, secondary forming becomes difficult.

The bulk density is preferably 0.03 to 0.3 g/d.

If the bulk density is less than 0.03 g/d, the sheet may be torn during secondary foaming or the strength of the molded product may not be sufficient;
If it is larger than j, the merits as a foamed product will be reduced.

When foaming styrene resin to obtain styrene resin foam, nucleating agents such as talc and calcium carbonate to control the foam cell diameter, plasticizers, lubricants, pigments, antistatic agents, antioxidants, flame retardants, etc. may be used in combination. Furthermore, in order to change the surface properties of the obtained styrenic resin foam, an antistatic agent, a lubricant such as silicone, etc. may be applied to the surface.

It is also possible to mix and use other styrenic polymers with the specific styrenic polymer into which the long alkyl chains have been introduced, as long as the functionality of the foam intended in the present invention is not impaired.

In order to heat and secondary foam the styrene resin foam obtained as described above, the styrenic resin foam is placed in a heating furnace, softened and secondary foamed, and then taken out of the heating furnace.
Generally, the product is immediately press-molded using a press mold to form a molded product.

The styrenic resin foam of the present invention can obtain a uniform softening state over a wide heating temperature range, so
Keloid-like formations due to temperature distribution etc. in the heating furnace are less likely to occur, and molded products with good shaping properties can be obtained, and in particular, molded products with excellent findability can be obtained.

EXAMPLES Hereinafter, the present invention will be specifically explained based on Examples, but these are not intended to limit the scope of the present invention.

Example 1 Styrene single F 90% by weight, ethylbenzene 10% by weight
To 100 parts by weight of the mixed solution, 0.5 parts by weight of an initiator having the following repeating unit was added, and the mixture was heated at 110°C for 6 hours.
Polymerization was carried out at 145°C for 5 hours, and unreacted styrene monomers, ethylbenzene, etc. were devolatilized at 230°C and 3 mmHg to obtain polystyrene. The analytical values are shown in Table 1.

The initial relaxation modulus of this polystyrene was measured according to the method described in Katsuyama et al., Wangka Journal, Vol. 71, No. 4, pp. 540-545 (1968), and the initial relaxation modulus was measured at 150°C. O
X I O'dyn/c4.1゜OX l at 120℃
The value of O”dyn/cd was obtained.

This polystyrene was mixed in advance with 0.25% by weight of talc, supplied to a 50 mmφ extruder, and melted at 205°C. 5% by weight of Freon-12 was press-fitted into the tip of the extruder, led to a second extruder, and cooled to 150°C.

Next, a cylindrical foam sheet was obtained from a circular gui, and 1
Incisions were made at two locations to obtain a thickness of 2.0 mm and a bulk density of 0.12/c.
- A styrenic resin foam sheet was obtained. This styrene resin foam was cured for one month, then heated to 125°C in an infrared heating furnace attached to the Illich molding machine to cause secondary foaming, and while changing the heating time, molded products with deep drawing parts were formed. The sheets were molded and the secondary moldability of each sheet was evaluated. The evaluation results are shown in Table 1.

Example 2 An experiment was carried out in the same manner as in Example 1, except that 100 parts by weight of a mixed solution of 97% by weight of styrene monomer and 3% by weight of ethylbenzene was used. The results are shown in Table 1.

Comparative Example 1 Styrene monomer 90% by weight, ethylbenzene 10% by weight
The mixture was incubated at 120°C for 6 hours without initiator for
The experiment was carried out in the same manner as in Example 1, except that the polymerization was carried out at 50°C for 5 hours. The results are shown in Table 1.

Comparative Example 2; 0.3 parts by weight of L-butylperhenzoate was added to 100 parts by weight of a mixed solution of 97% of L-chile 7 monomer and 3% by weight of ethylbenzene, and the mixture was incubated at 100°C for 6 hours at 140°C. The experiment was carried out in the same manner as in Example 1, except that the polymerization was carried out for 5 hours. The results are shown in Table 1.

(Effects of the Invention) The styrenic resin foam of the present invention does not cause breakage or crusting on the surface even with a short heating time during secondary molding, has good moldability, and has a long heating time. Also, molded products are less prone to sagging or keloid formation, and can withstand deep drawing under a wide range of conditions.

(1 other person)

Claims (2)

[Claims] (1) Weight average molecular weight is 150,000 to 500,000, and 12
Excellent secondary formability, characterized in that the ratio of the initial relaxation modulus of stress relaxation measured at 0°C and the initial relaxation modulus of stress relaxation measured at 150°C is in the range of 1 to 2.5. Styrenic resin foam. (2) The thickness of the styrene resin foam is 0.5 to 5 mm,
The styrenic resin foam according to claim 1, which is in the form of a sheet having a bulk density of 0.03 to 0.3 g/cm^3.